Method and apparatus for determining the thermal internal resistance in semiconductors of the same type

ABSTRACT

For determining the internal thermal resistance of a semiconductor wafer, an arrangement is provided in which a metal member supports the bottom of the wafer and a thermosensor contacts the underside of the member and monitors heat transfer from the wafer to the support member which is a function of the internal thermal resistance of the semiconductor. A current pulse is fed to the semiconductor causing heat to generate therein. The detected time interval between cessation of the pulse and detection of maximum heat transfer to the thermosensor leads to determination of the internal thermal resistance.

United States Patent 1 Belzer et al.

[ METHOD AND APPARATUS FOR DETERMINING THE THERMAL INTERNAL RESISTANCEIN SEMICONDUCTORS OF THE SAME TYPE Inventors: Hans-Joachim Belzer;Gerhard Kuhitzki, both of Belecke, Germany Assignee: LicentiaPatent-Verwaltungs-Gmbll,

Frankfurt, Germany Filed: Sept. 7, 1971 Appl. No.: 178,189

[30] Foreign Application Priority Data Sept. 7, 1970 Germany P 20 44225.5

US. Cl. 324/158 T, 73/15 A, 324/158 D lntLCl. G0lr 31/26, GOln 25/00Field of Search 324/158 D, 158 R,

324/158 T; 73/15 R, 15 A References Cited OTHER PUBLICATIONS Gates etal.; The Measurement Semiconductor Products; July 1959; pgs. 2l-26.

[ 11 3,745,460 [451 July 10,1973

Carslaw et al.; Conduction of Heat Oxford, 1947; pgs. 1,112-141.

Sidles et 21].; Thermal Diffusivity Jour. of Aplied Physics; Vol. 25;No. 1; Jan. 1954; pgs. 58-66. Powell, R. W.; Experiments Using Journalof Sci. Instruments; Vol. 34; Dec. 1957; pgs. 485-492.

Primary ExaminerRud0lph V. Rolinec Assistant Examiner-Ernest F. KarlsenAttorney-George H Spencer et al.

[5 7] ABSTRACT For determining the internal thermal resistance of asemiconductor wafer, an arrangement is provided in which a metal membersupports the bottom of the wafer and a thermosensor contacts theunderside of the member and monitors heat transfer from the wafer to thesupport member which is a function of the internal thermal resistance ofthe semiconductor. A current pulse is fed to the semiconductor causingheat to generate therein. The detected time interval between cessationof the pulse and detection of maximum heat transfer to the thermosensorleads to determination of the internal thermal resistance.

10 Claims, 4 Drawing Figures AMPLIFIER METHOD AND APPARATUS FORDETERMINING THE THERMAL INTERNAL RESISTANCE IN SEMICONDUCTORS OF THESAME TYPE BACKGROUND OF THE INVENTION The present invention relates to amethod and apparatus for quickly determining the internal thermalresistance of semiconductor devices of the same type having asemiconductor wafer.

The known indirect methods for determining semiconductor internalthermal resistance R as well as barrier layer temperature 8,, are basedon the assumption that the relationship between the increase intemperature A8 in a semiconductor wafer, relative to the wafer supportat a temperature 8 resulting from a certain electrical load across thebarrier layer, and the semiconductor electrical losses P, is similar tothat between the voltage and current of a circuit. The temper atureincrease can be expressed as:

Simplified, the assumption is that the heat loss resulting in thesemiconductor wafer under load originates from a concentrated heatsource which has the characteristic of an electric current source.Locally differing temperatures in the semiconductor wafer are combinedin a single actual value (barrier layer temperature 8 The differencebetween the barrier layer temperature and the wafer support temperaturethen corresponds to the terminal voltage of the heat source and themagnitude of this difference is determined by the heat flow impedance.This impedance has the characteristic of a resistive-capacitiveimpedance and is a representation of the heat conducting and storingcapability of the semiconductor layers in the path of the heat flow. Thethermal behavior of a pulse-charged semiconductor device can thus becompared with the electrical behavior of a correspondingly pulse-chargedimpedance which should be imagined to be a chain conductor consisting ofa plurality of RC members.

According to the known indirect methods, the internal thermal resistanceis determined in continuous operation with a constant thermal energyloss. Since the heat storing capability due to the attainment of thesteady state has no effect here, these methods are based on theabove-mentioned relationship. To determine therefrom the internalthermal resistance, the values of the energy loss I., and the wafersupport temperature 8,, are measured directly, and the barrier layertemperature 8,, is determined with the aid of the previouslydeterminable relationship between 8,, and the forward voltage drop witha low constant forward measuring current, this constituting ameasurement of the forward voltage, or the temperature 8,, is measuredat different forward losses and the temperature 8,, is eliminatedtherefrom.

A newer method utilizes the fact that during intermittent continuousoperation with constant energy loss the temperature 8,, and thetemperature 8,, and thus also the temperature difference (8,, 8 is keptconstant, and the internal thermal resistance is read from a gauge whichmeasures the forward energy loss but is calibrated for the Rmeasurement. In the intervals of the intermittent continuous operation,the test object is charged with a low forward current to determine andkeep constant the temperature 8,, and the forward voltage is measured.This method has the advantage over the older methods that it permitsfaster and substantially' more dependable measurement of the internalthermal resistance. Certain additional considerations for control meansmust here be considered, however.

In all the above-described methods the measurement is being made duringcontinuous operation of the semiconductor, with constant energy loss.Thus, the respective measuring results do not reflect the exemplarythermal behavior as it would occur under a pulse-type load. Thisbehavior may be determined, for example, by the effect of impurities inthe crystal structure of the semiconductor wafer which may producetemporary local heat accumulations. Particularly for thyristors whichare to be used in pulsed current rectifiers, it is important, often evendecisive, that the thermal behavior during pulse-type loads bedetermined. Moreover, in many thyristors the transmission characteristicexhibits irregular jumps in the lower current region so that it isimpossible to determine an unequivocal association between the forwardcurrent and the forward voltage. In such cases it is thus impossible tomeasure the barrier layer temperature according to the known Rdetermination methods and much less to maintain it constant.

SUMMARY OF THE INVENTION The present invention provides a method fordetermining the intemal thermal resistance in semiconductor devices ofthe same type, such. devices include thyristors and rectifier diodes.The present invention determines the thermal behavior of a test objectunder pulse-type loads without influencing and measuring the barrierlayer temperature. Thermal behavior is measured by recognizing acorrelation with the internal thermal resistance which is determinedaccording to an indirect measuring method employing a constant load withconstant energy loss. With the method according to the presentinvention, each tested semiconductor device is charged with a currentpulse having an amplitude which almost reaches the current surge limitof the device and of such a short pulse duration that at the end of thispulse, heat due to the pulse cannot yet be measured at a wafer supportin the form of a housing bottom. The measuring point is as close aspossible to the interface between the semiconductor wafer and thehousing bottom. The time expiring between the end of the current pulseand the maximum of a resulting temperature pulse occurring after thecurrent pulseis measured and used as a direct measure for the evaluationof the internal thermal resistance. t

The present invention also provides a thermoelectric temperature sensor,which has a low time constant compared to the duration of thetemperaturepulse, a high effectiveness, and a high thermal resistance but a lowheat transfer resistance at the measuring point on the housing bottom.This thermosensor is used to con vert the temperature pulse into ananalog electrical signal and this signal is differentiated and amplifiedand then fed to a comparator which feeds a dc. voltage signal ofunchanging polarity to a digital counter. The counter is started. at theend of the current pulse to measure the expiring time as long as thepolarity of the the type of the device. Due to the short time requiredfor this test, semiconductor devices of a series can be individuallytested in succession. However, a plurality of semiconductor devices of aseries can be successively checked in groups or at random if theappropriate number of testing devices and measuring sensors areprovided. An arrangement constructed according to an embodiment of thepresent invention with a thermoelement usable as a temperature sensorfor accomplishing the method of the invention for individually testingthe semiconductor devices will be explained in detail in the descriptionof the invention provided below.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partly pictorial, partlyschematic representation of a device for testing the R of an individualsemiconductor device according to the invention.

FIG. 2 is a cross-sectional view of the configuration of thermoelementsused as a temperature sensor for performing the method according to thepresent invention.

FIG. 3 is a series of diagrams used in explaining the method of theinvention.

FIG. 4 is a diagram showing the correlation for a device randomlyselected from a series of semiconductor diodes of the type D 300,between the R measured under steady state conditions according to aknown indirect method and the time measured according to the method ofthe present invention between the end of a current pulse and the maximumof a resulting temperature pulse. The designation D 300 signifies a typeof power-diode, which is rated for a limiting average onstate current of300 Amperes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The R of a semiconductor deviceis known to be determined by the heat transfer conditions in thejunction between the semiconductor wafer and a supporting member, whichjunction is generally effected by soldering. The electrical energy whichhas been converted into heat in the semiconductor wafer substantiallyflows through the large-area junction between the wafer and thesupporting member, in the form of a housing bottom. As already explainedabove, faulty heat junctions between semiconductor wafer and housingbottom can be determined according to the known determination methodwith satisfactory accuracy only at a great loss of time since a thermalequilibrium must be obtained in each case. When the heat transfer isdetermined according to the method of the present invention this is notnecessary. It is only assumed that this method is employed for devicesof the same type under the same conditions. This prerequisite is basedon the fact referring to FIG. 1, that for devices of the same type, themass m of the semiconductor wafer P and the mass m, of the wafer supportconstituting the housing bottom are constant and that they are made ofthe same material, and also on the fact that it is practically only themass m; of the housing bottom and no other housing portions or coolingmembers which are in thermal contact with the mass m of thesemiconductor wafer. The R is determined for a device in which thesemiconductor wafer is completely connected with the housing bottom aswell with the required terminals 1 and 2. The housing bottom is incontact only along a narrow edge zone with a perforated steel plate 3provided for mounting the test object in the testing arrangement. Theobject to be tested is fastened by means of a copper ring 4 which isprovided as the current connection and which is pressed by a pneumaticcylinder 5 via an insulating tube 6 against the upper side of thehousing bottom. If required, a copper ring can also be arranged betweenthe steel plate 3 and the housing bottom so that a minimum of heat isremoved from the test object when it is mounted. I-Ieat dissipation byradiation and convection can here be neglected. The lateral edge surfaceof the housing bottom extends through a rigid woven disc 7 to center thetest object. The semiconductor terminals 1 and 2 are inserted throughthe insulating tube 6 via an opening in the tube.

A significant requirement for the use of the method of the presentinvention is that the semiconductor wafer is charged with a currentpulse I as in FIG. 1, during such a short time that the device issufficiently heated before noticeable heat with, or transfer to, thehousing bottom takes place. It has been found that a pulse duration ofapproximately 10 ms with a current pulse having an amplitude near thepermissible current surge limit I of the device P fully meets thisrequirement.

The heat transfer which then takes place between the semiconductor waferand the housing bottom is apparent in the time function 8,, (t) of thehousing bottom temperature which begins, at the end of the currentpulse, at the level of the ambient temperature, then increases up to amaximum 8 and finally drops to a level 8' which is higher than theambient temperature. The heat exchange is completed at 8' and thehousing bottom and semiconductor wafer have the same temperature 8.

The course of the temperature pulse leading to heat compensation dependsin part on the thermal resistance between the semiconductor wafer andthe housing bottom and on the thermal capacities of the masses m and mtaking part in the heat exchange, and partially also on the location ofthe temperature measuring point on the housing bottom.

In the center M of the underside of the housing bottom, the temperaturepulse is highest and shortest when the thermal resistance is uniformalong the entire connecting surface between semiconductor wafer andhousing bottom. This center is thus the most favorable measuring pointfrom a technilogical point of view. The thermal transfer resistance Rinfluences the position and amplitude of the temperature maximum 8 ofthe temperature pulse 8 (t) measured at the same measuringpoint-Temperature conductivity and thermal capacity of the masses m andm also make their influence felt but can be considered to be constantfor test objects of the same type. The time location La of thetemperature maximum which is symbatic with the height of the maximum inan inverse relation can thus be considered the characteristic dependentof the thermal junction resistance T in test objects of the same type. Aresult of the invention is that the time position of the temperaturemaximum is independent of the energy of the current pulse.

An additional significant requirement for the use of the above-describedmethod according to the present invention is that no noticeable,measurable, heat will be removed from the housing bottom during thetemperature measurement at measuring point M. Further, the heat transferresistance between measuring point M and temperature sensor Th is keptconstant and sufficiently low. This requirement is decisive with respectto the realization of reproduceable measuring results. It issatisfactorily met with the use of oppositely poled ther' moelements Th1and Th2, constituting temperature sensor Th, having a total of threesensing arms.

According to FIG. 2 the first arm is formed of a silicon pin 8, thecommon arm of the two thermoelements Th1 and Th2 is formed by thehousing bottom of the semiconductor device test object, and the thirdarm by three steel pins 9, and 10, and another not shown, which areelectrically connected together. Silicon pin 8 is conically ground atone end and flattened at the peak of the cone so that the brittlesilicon material will not break. Silicon pin 8 then has its tip incontact with the housing bottom at the measuring point M so that thethermal connection for Th1 is formed. The three steel pins are arrangedat a very slight spacing from, and symmetrically around, silicon pin 8and also contact the housing bottom at measuring point M so that thethermal connection for Th2 is established.

With this arrangement the thermal connections which are thus formed aresubjected to the same temperature, measuring temperature 8, so that thetemperature sensor voltage U resulting from the difference between thethermal voltages of Th1 and Th2 is independent of temperaturefluctuations as well as of the temperature distribution over the housingbottom. With this arrangement no undefinable temperature differences canoccur between temperature sensor Th and measuring point M.

The tip of silicon pin 8 is an excellent heat contact with the housingbottom but due to the poor heat conductance of silicon, practically noheat is removed from measuring point M. These properties assure goodreproduceability of the temperature measurement. The relatively highthermal capacity of the silicon has a favorable effect on thethermoelectric temperature measurement so that the temperature sensorexhibits a comparatively high degree of efficiency. Furthermore, thearrangement of the three steel pins with respect to the silicon pin 8substantially eliminates ambient interfering influences on thetemperature sensor voltage UT).

The thermosensor of FIG. 2 consists of a steel tube 1 l which is closedat one end except for passage of lead 14 carrying the sensor voltage UAn insulating tube 12 is disposed within tube 11 and the other end ofthe tube is provided with a brass sleeve 13 into which the silicon pin 8is fitted. Lead 14 passes through tube 11 and is electrically connectedwith brass sleeve 13. Although not shown, lead 14 is provided with ashielding connected to the steel tube 11 at a point such as 14a. Fromthe open upper end of steel tube 11, the three steel pins extendupwardly beyond silicon pin 8 and are mounted to be resilient in theaxial direction. A perforated disc D prevents these pinsfrom falling outand presses the insulating tube 12, via an insulating disc, against ahard rubber plate R so that the silicon pin 8 is immovably fixed.

The thermosensor Th is perpendicular to the housing bottom and isaxially displaceable, guided by a further brass sleeve 15. By means of apressure cylinder 16, the

contact pressure of the pin 8 against the housing bottom is adjustable.The guide sleeve 15 is fastened to a support 17 in a suitable manner sothat the thermosensor Th can be adjustably positioned along the housingbottom.

In order to describe the method according to the present invention forthe purely qualitative representa tion, and for the quantitativedetermination, of the thermal internal resistance for a single objectfrom a batch of identical semiconductor devices, reference is now madeto the diagrams of FIG. 3. After the test object is. inserted into theabove-described testing arrangement and the thermosensor Th is alignedto the most favorable measuring point M in the center of the housingbottom surface, the test object is supplied with a forward current pulse1,.(1) over lead 30 then to ring 4 of FIG. 1 to the test object. Thepulse is of approximately 10 ms duration and has an amplitude no greaterthan the permissible surge current value I for the test object. The timesequence of this pulse is illustrated in diagram a. Viewing FIG. 1, sucha current pulse may be produced, for example, by discharging a capacitor18 via a choke l9 and an attenuation resistance 20 connected to lead 1.

Returning to FIG. 3, after time t when the current pulse I ceases, heatproduced in the semiconductor wafer is transferred via the thermaltransfer resistance existing in the junction between the wafer and thehousing bottom, to the measuring point M of the housing bottom with adelay. A temperature pulse 8 (t) is produced which has thecharacteristic shown in diagram b. This pulse which will reach a pulseamplitude of 1 to 2 degrees depending on the type of test object, issensed by the thennosensor Th and converted into an analog pulse-shapedvoltage U,,,(t), as shown in diagram c. Since the interval betweenthetime ts of the temperature maximum 8,, and the time t can be used as thecharacteristic equivalent value for the internal thermal resistance Rthe pulse-shaped thermal voltage U,,,(t is fed via a differentiatingstage 21 (FIG. 1) to an amplifier 22. At the output of the amplifier 22there results a signal vU,,,(t) as shown in diagram d. There is a pointin time when this signal has a polarity change, or zero cross-over,which coincides with the time tsmax,

A step voltage signal is generated by cross-over detector 23 of FIG. 1,as shown in diagram e, which has the same polarity as the amplifiedsignal until the latter changes its polarity. A count stop signal isthen produced by the detector 23 at the step change. The stop signal isfed to a digital counter 24 which had beeh started by a set and startsignal presented by the end of pulse l attime t The set signal istransmitted along lead 32. The duration of the count (ta y-tn) thus Rcan thus bemeasured.

Depending on the type of the semiconductor device undergoing thetesting, the time interval may be between 50 and 500 ms so that theentire process each time takes at most one-half a second. The countingincrements of the digital counter 24 are sufiiciently short, e.g. aslong,.so that R can be measured very accurately. Diagram f shows thecounting pulses of digital counter 24 as a broken line.

It should .be noted with respect to the described means for performingthe method of the present invention that in spite of the highsensitivity of the temperature sensor Th employed, which has only twothermojunctions, the thermal voltage is still low. This requires a highdegree of amplification for amplifier 22 and deand tector 23. Zero pointfluctuations may thus occur which lead to signal distortions in theamplifier and to a drifting of the stop signal in the detector.

The amplifier noise may also adversely influence the accuracy of thetime measurement. The drift, however, can be easily controlled. Theshort time required for the method further provides for room formultiple repetition of the process which also makes it possible toobtain an exactly averaged result. A further advantage of the method isthat one can always start with any given temperature state of thehousing bottom. The time duration (tfimax to) thus determined initiallyfurnishes a qualitative indication of the internal thermal resistance.

For the quantitative determination of the same, use may be made ofempirically secured correlations, specific to the particularsemiconductor type employed, between the values R determined accordingto known methods and the time difference maX l0 measured according tothe method of the present invention. As an example for this, FIG. 4shows the correlation for a number of semiconductor diodes of the type D300. In this diagram, the plot should be considered to be linear in arange which goes beyond the highest permissible R value marked G. Basedon this linearity, the time difference to be read at pulse counter 24can be scaled and given directly as the R value.

The method of the present invention brings further advantages. Since theindividual determinations can be rapidly made, they can easily beautomated. The apparatus required for this is relatively simple. Themethod opens the possibility of sensing and checking the homogeneity ofthe internal thermal resistance over the junction surfaces between thesemiconductor wafer and the housing bottom by means of the thermosensorTh. Such tests are significant particularly with large-area devices, forexample for locating so-called shrinkholes. Also, the blocking voltageof a test object can be controlled immediately before and after acurrent pulse. Transmission characteristics with jumps in them will notbe incorporated into the measuring result.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

We claim:

1. A method for determining the internal thermal resistance for asemiconductor device composed of a semiconductor wafer and an underlyingsupport member connected thereto, comprising the steps of:

subjecting the wafer to a current pulse having a duration that issufficiently short to prevent measurable heat transfer to the supportmember during the occurrence of the pulse;

monitoring the temperature of the support member at a point thereof; and

measuring the time interval between the end of the pulse and attainmentof maximum temperature of the support member at the measuring point, toprovide a measurement on the basis of which the internal thermalresistance can be determined, said step of measuring being carried outby: converting the temperature changes in the support member into anelectrical analog signal having a maximum point corresponding to the endof the measured time interval; subjecting the analog signal todifferentiation to form a differentiated signal having a polaritycross-over point coincident to the maximum point of the analog signal;and detecting the crossover point which represents termination of thetime interval.

2. The method of claim 1 wherein the pulse has an amplitude approachingthe current surge limit of the wafer.

3. The method of claim 2 wherein the temperature monitoring point forthe support member is selected as close as possible to the junctionbetween the member and wafer.

4. Apparatus for determining the internal resistance of a semiconductordevice composed of a wafer and associated conductive support member,comprising, in combination:

means connected to the wafer for current pulsing the.

wafer with at least one pulse;

means connected in heat transfer relation to the support member forsensing a resulting temperature rise in the support member andgenerating a corresponding analog signal; means connected to saidsensing means for differentiating the analog signal to form adifferentiated signal having a polarity cross-over occurringsimultaneously with maximum temperature in the support member; and

means connected to said pulsing means and said differentiating means andresponsive to the end of the current pulse and the occurrence of suchcrossover for measuring the interval therebetween;

whereby the measured interval can be directly correlated to the internalthermal resistance of the de- VlCe- 5. An arrangement as defined inclaim 4 wherein said sensing means comprises a thermoelectrictemperature sensor having a low time constant compared to the durationof the temperature rise in the member, a high efficiency, a high heatresistance, and a low heat transfer resistance.

6. An arrangement as defined in claim 4 wherein each current pulse is ofa duration which is relatively short, thereby precluding noticeabletransfer of heat from the wafer to the member until termination of thepulse.

7. An arrangement as defined in claim 6 wherein the amplitude of thepulse approaches the surge current limit of the wafer.

8. An arrangement as defined in claim 7 wherein said interval measuringmeans comprise a counter connected for providing a representation of theinterval being measured;

means connected for initiating operation of said counter in response totermination of the pulse;

means for detecting the polarity cross-over; and 7 means connecting saiddetecting means to said counter for stopping the operation of saidcounter when cross-over occurs, thereby measuring the interval.

9. An arrangement as defined in claim 8 wherein said support member isconstituted by a housing bottom, and further comprising:

conductive means mounted in contact with an annular region of saidhousing bottom; and

circuit means connected between the wafer and said conductive means totransmit current pulses to the semiconductor device.

10. An arrangement as defined in claim 9 further comprising meansconnected for adjusting the contact pressure between the housing bottomand said sensing means.

1. A method for determining the internal thermal resistance for asemiconductor device composed of a semiconductor wafer and an underlyingsupport member connected thereto, comprising the steps of: subjectingthe wafer to a current pulse having a duration that is sufficientlyshort to prevent measurable heat transfer to the support member duringthe occurrence of the pulse; monitoring the temperature of the supportmember at a point thereof; and measuring the time interval between theend of the pulse and attainment of maximum temperature of the supportmember at the measuring point, to provide a measurement on the basis ofwhich the internal thermal resistance can be determined, said step ofmeasuring being carried out by: converting the temperature changes inthe support member into an electrical analog signal having a maximumpoint corresponding to the end of the measured time interval; subjectingthe analog signal to differentiation to form a differentiated signalhaving a polarity cross-over point coincident to the maximum point ofthe analog signal; and detecting the cross-over point which representstermination of the time interval.
 2. The method of claim 1 wherein thepulse has an amplitude approaching the current surge limit of the wafer.3. The method of claim 2 wherein the temperature monitoring point forthe support member is selected as close as possible to the junctionbetween the member and wafer.
 4. Apparatus for determining the internalresistance of a semiconductor device composed of a wafer and associatedconductive support member, comprising, in combination: means connectedto the wafer for current pulsing the wafer with at least one pulse;means connected in heat transfer relation to the support member forsensing a resulting temperature rise in the support member andgenerating a corresponding analog signal; means connected to saidsensing means for differentiating the analog signal to form adifferentiated signal having a polarity cross-over occurringsimultaneously with maximum temperature in the support member; and meansconnected to said pulsing means and said differentiating means andresponsive to the end of the current pulse and the occurrence of suchcross-over for measuring the interval therebetween; whereby the measuredinterval can be directly correlated to the internal thermal resistanceof the device.
 5. An arrangement as defined in claim 4 wherein saidsensing means comprises a thermoelectric temperature sensor having a lowtime constant compared to the duration Of the temperature rise in themember, a high efficiency, a high heat resistance, and a low heattransfer resistance.
 6. An arrangement as defined in claim 4 whereineach current pulse is of a duration which is relatively short, therebyprecluding noticeable transfer of heat from the wafer to the memberuntil termination of the pulse.
 7. An arrangement as defined in claim 6wherein the amplitude of the pulse approaches the surge current limit ofthe wafer.
 8. An arrangement as defined in claim 7 wherein said intervalmeasuring means comprise a counter connected for providing arepresentation of the interval being measured; means connected forinitiating operation of said counter in response to termination of thepulse; means for detecting the polarity cross-over; and means connectingsaid detecting means to said counter for stopping the operation of saidcounter when cross-over occurs, thereby measuring the interval.
 9. Anarrangement as defined in claim 8 wherein said support member isconstituted by a housing bottom, and further comprising: conductivemeans mounted in contact with an annular region of said housing bottom;and circuit means connected between the wafer and said conductive meansto transmit current pulses to the semiconductor device.
 10. Anarrangement as defined in claim 9 further comprising means connected foradjusting the contact pressure between the housing bottom and saidsensing means.